Ground levelling, Drainage and Soil enrichment

This chapter discusses the "underlying" drainage-system as part of Construction of the Infrastructure and ground levelling. Very much "underlying" because most of it sits under the ground-surface and is not directly visible. Placing the infrastructure is done together with levelling the ground surface and where applicable enriching and conditioning the soil.

Ground surface levelling and soil enrichment of the Ginshanada, gravel surfaces, the Tsukiyama sections and areas to be paved. Because most of the infrastructure cabling, hoses and pipes is put under the surface, this work is done in combination with the construction of the primary infrastructure facilities.
Paving, garden-wall construction and veranda, duckboard an path foundation preparation are directly related to the above construction work and need to be taken into account and carefully planed together.
The following ground-plan shows the network of cables, pipes and wires and will be referenced in the elaborating sections below.

Tsubo-en network

This is how the garden looked just after delivery of the house. Note the absence of houses between our house and the wood to the east (front garden direction).

The soil you see is very much clay. Nor sea-clay that lies just under the lower surface here.
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Here we ran into an interesting "small print" phenomenon in the purchase contract.

When the house was delivered we found this hole in the garden. Inquiry learned that this was in line with the agreement which stated that the lot would get levelled with original soil only. This did not only relate to the quality of the soil but also to the amount.

As you can see we had a substantial shortage of this "brown gold".
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Prior to any other garden activity, the first activity was getting the "hole" fixed. This is nothing you can do later or on your own.

This required a couple of truck loads soil that also carried the first mole into the garden.
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Except for placing Mount Sumeru this was last time ever that machinery like this was used in the garden. 99apr23
Spade and turnover the whole garden area where planting will be growing, that is actually the whole are we call the Tsukiyama. 99apr24

Ginshanada levelling and the drainage-system

The flat gravel areas do not need to get enriched as we do not want to grow anything on it. Levelling, sloping and draining the Ginshanada i.e. gravel area basis or substratum is required to ensure that it will show and remain flat and level to the eye and it will not turn into a swamp or pond.
Depending on your location and soil, at least a simple drain system, just under the barrier cloth will be required. We decided that we for sure need a drainage-system and a number of drain lines (see the plan), the longest one in the middle of the main ginshanada from front to back as well as some shorter ones. Some of these will also take care of draining the main O-karikomiarea and are not as such under the gravel area but laid in the tsukiyama soil (see below).

Ginshanada levels


We tamped the ground with minor sloping in such way that we will have a positive drain and rain water runs toward the drain-pipes (yellow lines on the groundplan).
The drain-pipe we used is 80 mm round (3 inch). The drain ditches are 15 to 20 cm (6 to 8 inch) wide and deep and have a sloping grade of 1 cm per 2 meter (say 1/2 inch every 8 feet). This however very much depends on what you can effort, that is how deep you can go.
In our case the longest drain line has an outlet on both ends, hence we can go deeper than you may be able to go. At one end we have the street-level that is about 8 to 10 cm (3 to 4 inch) lower than the front garden gravel area. The other end, in the back, is even less of a problem as the level of the waterway is about 2 meter (6 feet) under our garden level.
Then we put a 2 cm (0.8 inch) layer of drain stone, or sand if you like, on the bottom of the ditch and lay the drain-pipe on top of it. The ditch for the drain-pipe was filled-up with sand (can be don with drain stone) and sand was also used to compensate for the fall we created in the original clay surface.

We did tamp all the gravel area and covered it with good quality barrier cloth (or weed control or landscape fabric). Since the gravel areas are not square, there is a lot of fabric overlap. We cut out overlap so as to minimize the number of wrinkles. Loose ends are held down by long pins, nails or screws. Where the landscape fabric engages with the tsukiyama shores we have dug it into the ground, straight down for some 20 centimeter ( 8 inch). This will prevent the groundcover of growing under it and also hold it down as long as there is no gravel on top of it.

In front a roll weed control fabric.
Marijke is busy digging the drain-pipe ditch.
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As you can see on the groundplan in Design the architecture or in the Table of Contents, in the center-back we have four drain-pipes next to each other.

Be sure to document where your pipes and cables lay in the ground as this can become essential information at a later stage.
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It took many days to shuffle the truck load, 10 m2, of gravel into the wheelbarrow and carry it to the area of its final destination. 990101
As shown in the above construction diagram almost halve of our ginshanada boundary is formed by the wall of the house. Here we have actually added an additional plastic band that stands up against the wall. In addition it is supported by a kerb, level with the ground and pushed against the wall.

This is something we had not done initially. The result was that we lost a lot of gravel and had extra maintenance to do. The reason for this is that the soil not only "sinks" but also "floats", moves away from the house. At a certain stage the gravel on top of the weed control fabric got too heavy and fell into this groove.
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Here the work on the wall in the front garden has just completed, the Tsukiyama, Turtle Island and Ginshanada have been levelled and the first gravel distributed.
No planting yet.

The greenbelt in front of our lot is still untouched.
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An other view in the front garden to be, right from the driveway.

The concrete-tile path that came standard with the house was removed to make place for a real Roji (photo: 1999).
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In the back you see the first Buxus plants that have just arrived. These form the basis for our O-karikomi and hako-zukuri "sculpture".
In front the gravel ready for further spreading.
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Two drain-pipes exiting to the water bank via the retaining wall (see Walls, retaining walls and stairs). 1229
After having been spread out this is the first time the gravel gets raked flat. It will need a number of rain showers before the gravel has settled enough (Dutch: inklinken) to leave a minimum of footprint behind after being walked on. 9901


As discussed in The Ginshanada, we used pea gravel (2 to 8 mm pebbles) even although we know that the round surfaces are harder to rake into patterns and patterns more easily wash away in heavy rains. This is really a matter of availability (back in 1998 that is).
If you can get hold of a sharp or broken gravel in the sizes and colors you want that would even be better.
Purchase enough of the gravel of your choice to cover your Ginshanada with a 4 to 5 cm ( 1.5 to 2 inch) thick layer and to have some spare. If later on you would need some additional material it will be impossible to get it exactly the same. We choice this thickness as this is thick enough to be raked in patterns or flat and also not to thick to walk on while leaving behind no or only a minor impression.

For additional remarks on gravel selection, patterns and raking see: The Ginshanada gravel area.

To show prove that the "prevent it from becoming a swamp or pond" is not exaggerated here you see some photos taken hours after a serious combined rain shower and hailstorm. 0612
Note that this is with the drainage-system in full operation !

The "Turtle island" in the front garden has now become as real an island as it can get.
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In addition to the gravel area drainage we have a number of drainage pipes laying in the tsukiyama, in particular for draining the main O-karikomi area. These are not as such under the gravel area but laid in the tsukiyama soil.

So as to make maximum use of these the inlet of these pipes is level with the gravel surface, either just under or next to the gravel.
To prevent gravel and debris getting into these pipes we have covered the inlet with insect screen cloth and then filled the hole in front with drain stone. Then covered it up with gravel to make it invisible.

These photo's where taken later hence the planting and roots.
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As indicated above some of the drain-pipes need to take care of draining the main O-karikomi and the left side compartment, and are not as such under the gravel area but laid in the tsukiyama soil.
Where the drain-pipe openings are at surface level, filtering tissue prevents the pipes of blockage by gravel and debris.
Important:
These filters need annual cleaning.





Levelling and enriching theTsukiyama soil

Levelling and enriching the Tsukiyama area's is done in conjunction with the work on the "flat" gravel surfaces as described above.

Soil types are described according to their main constituents. Thus, soil with a lot of sand is a sandy soil; soil with a lot of clay is a clay soil; and soil with a lot of organic material is an organic soil. If the organic material is peat, it is generally called peaty soil.
If soil has a good balance of all the important constituents that is sand, silt, clay and organic material and no preponderance of any one of them, it is called a "loam". It might tend a little towards sand or clay and this would define it as a "sandy loam" or "clay loam". The latter is more or less what we have as the upper layer. Under the upper layer we have the original sea bottom soil which is sea-clay, almost white of color. The color is caused by chalk from the shells contained in the soil. A high, but not comparable, concentration of (whole) shells and chalk is also found in our upper soil layer. Hence we needed to "enrich" it with sand and organic material. For the latter we used humus.

How you need to enrich your ground you need to carefully investigate. It will be easy to find guidelines for that on the many gardening sites on the web.

At the right site, the back and in front of our house we have the Ginshanada (silver sand open sea) with in the back right corner (North), as shown on the ground plan below, the main O-karikomi (D) combined with Hako-zukuri.
See: The main O-karikomi for a description.


Level groundplan


On the above plan we have indicated the tsukiyama ground-heights of the whole garden. The Ginshanada gravel is our reference, level "0". The actual "visual heights" very much depend on the ground cover and planting. Even in area´s where the same ground covering plants are used there can be a difference in growing height of as much as 5 centimeter (2 inch). This is the case with the Leptinella potentillina (prev. Cotula) that is used in section A, C and G. For instance, the Chamaemelum nobile "Treneaguei" (Anthemis nobilis) (Dutch: Loopkamille) used in section E can get as high as 15 cm (6") where in some locations it remains under 2 cm (less than 1' ).

Clay is composed of very fine particles too, even finer that silt, and it is the result of the chemical decay of rocks as much as their physical breakdown. Clay is chemically active, which means that it can bind strongly to itself, and to other soil constituents. It bonds sand and silt together into tiny soil particles. The presence of a lot of clay and chalk causes too much binding, and the soil becomes a hard, lumpy mass. And that is what we had, and partly still encounter. 99apr29
We have manually spade the garden two spits deep. At least all the Tsukiyama area's, that is the surfaces where planting need to grow.

Enriching the soil was a manual activity. Here the humus that we mixed two spits deep through the upper soil-layer.
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Our bottom is rich of clay and chalk. In the ground we found "clay-plates" of white, blue and gray clay, that are 100% watertight.

As an extra measure for draining of planting areas we have drilled holes in the ground, using a ground-drill of 7 cm (2.7 inch) round, of over 1 meter (3.3 feet) deep, and filled these up with gravel and/or sand.
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Front garden:
This photo was taken in summer 1999 after the ground-work, paving and wall building had finished and the first planting had been planted.
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It is said that a healthy soil should contain worms, as they are a key element within the natural cycles that determine the soils structure. Worms create a good texture, drainage and incorporate organic matter into the soil by helping to turn it into humus. So if this is the criterion than we have an extremely healthy soil. We have so many worms that moss is hard to retain and even the groundcovers at some spots have hard times to survive.
Once you have added organic matter to the soil and solved any drainage troubles the worms should increase natural, but to increase the numbers add a few to a compost heap and watch them multiply over a few months.

What did not work well

Here we document what went wrong with regard to the groundwork and drainage-system.

  1. With regard to your purchase contract, not only "read the small print carefully" but be extremely cautious with the interpretation. Always be suspicious !
    Here we ran into an interesting "small print" phenomenon in the purchase contract. When the house was delivered we found the above depicted hole in the back garden. Inquiry learned that this was in line with the agreement which stated that the lot would get levelled with original soil. This did not only relate to the quality of the soil but also to the amount. As you can see on the above photo we had a substantial shortage of this "brown gold".
  2. As shown in the construction diagram almost halve of our ginshanada boundary is formed by the wall of the house. . What we did not expect to happen is that the soil not only "sinks" but also "floats", moves away from the house. At a certain stage the gravel on top of the weed control fabric got too heavy and started falling into this groove.
    Here we have actually added an additional plastic band that stands up against the wall. In addition it is supported by a kerb, level with the ground, and pushed against the wall.

    This is something we had not done initially. The result was that we lost a lot of gravel and had extra maintenance to do.

Links related to groundwork



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